Defect and Diffusion Forum Vols. 237-240

Abstract: Understanding of diffusion processes in polycrystalline solids is of importance for studying processes like oxidation, precipitation, creep, superplastic forming, annealing and many other processes. In this paper, we will introduce our latest software that is able to simulate the diffusion process in poly and nano-crystalline solids. The diffusion process is simulated based on Random Walk theory. The diffusion matrix can be computer generated or obtained from the experimental measurement using Orientation Imaging Microscopy. The software describes microstructure and incorporates the effects of the material’s texture, grain size and shape, grain boundary character distribution, statistical information on CSL boundary distributions, contribution from triple junctions and interfaces, the trapping of diffusing atoms and interaction of atoms with second phases and voids. A built-in database of diffusivities of various diffusing species and the user friendly interface make the software easy to use. The software is also applicable to thin films and multilayer structures. The output of simulation can be presented as a normalized concentration profile, a two-dimensional contour map of diffusing species, and also using many other statistical representations.

Abstract: A method of the determining of the mutual diffusion coefficients in ternary intermediate phases is suggested. Methodology for determination of the interdiffusion coefficients of phases formed in a ternary diffusion couple in T-sample configuration is presented. The method requires only one annealing of the T-sample and makes it possible to calculate the matrix of the diffusion coefficients in the (CuNi)6Sn5 and Cu3Sn ternary intermediate phases under low temperature. The concentration profiles and electron micrograph of the diffusion zone was obtained in the ternary Cu-Ni-Sn system annealed for 64 hours under 200°C. Phase competition in this ternary system with special configuration of T-sample leads to lateral diffusion of Cu, to formation (CuNi)6Sn5 compound between Ni-Sn side and to suppression of other NixSny intermediate phases.

Abstract: A new inverse method is applied for the determination of interdiffusion coefficients in b- NiAl(Pt) and b-NiAl(Pd). The results show that substitution of Pt or Pd to b-NiAl accelerates the diffusion of aluminium. Within the studied composition range and for Al-poor aluminides, the cross coefficients are negligible except for high Pd contents

Abstract: The application of the Danielewski-Holly model of interdiffusion for modelling of selective and concurrent oxidation of multi-component alloys is presented. This model enables prediction of the evolution of components distributions taking into account interdiffusion and the reactions at the boundary, e.g, due to the oxidation/sulphidation processes. The model is subsequently reformulated to the form suitable for numerical calculation. For illustrating its capabilities modelling of the selective oxidation of Ni-Pt alloys is presented. The results are compared with those obtained from Wagner model. Both models give exactly the same results for the longer reaction times. In Wagner model the equilibrium concentration of the elements at the boundary is reached instantly while in this model it changes with time. Consequently the model allows modelling of initial stages of oxidation.

Abstract: The impurity diffusion coefficients of Cu in Fe have been determined in the temperature range of 1073 - 1163 K by means of Laser Induced Breakdown Spectrometry (LIBS). The volume diffusion coefficients for Cu impurity diffusion in a-iron found in this work are in good agreement with the previously published result. The grain boundary diffusion coefficient gb D s d was also calculated using the volume diffusivity and processing the tails of the measured profiles. The values of the activation energy for volume and grain boundary diffusion were approximately 280 and 161 kJmol-1, respectively. This indicates the possibility of a monovacancy diffusion mechanism in case of volume diffusion. The results for the diffusion coefficients are Dv= 2.2 ×10-2exp(-280 kJmol-1/RT) m2s-1 and gb D s d = 2.6 ×10-11exp(-161 kJmol-1/RT) m3s-1.

Abstract: Iron bulk self-diffusion coefficients were measured in Fe2O3 single crystals using an original methodology based on the utilization of 57Fe stable isotope as iron tracer and depth profiling by secondary ion mass spectrometry (SIMS). The iron self-diffusion coefficients measured along c-axis direction, between 900 and 1100o C, in oxygen atmosphere, can be described by the following Arrhenius relationship: D(cm2/s)= 5.2x106 exp [-510 (kJ/mol)/RT], and are similar to reliable data available in the literature, obtained by means of radioactive techniques.